Eye tracking devices may be limited by their light gathering ability and thus use relatively large imaging sensors and lenses. This may limit their integration into mobile devices due to the resulting z-height (e.g., thickness).
Remote eye tracking may be based on detecting reflections of known light sources on the cornea and determining an edge of the pupil. There may be a trade-offs between these uses. For example, it may be easier and more robust to detect a pattern of multiple reflections but such a pattern may hide at least some of the edge of the pupil.
There are general needs for improved eye tracking.